1. Field of the Invention
The present invention relates to an image processing apparatus for obtaining a reproduced image of a high quality.
2. Related Background Art
It has already been proposed to reproduce an image including halftones with a dither method or a density pattern method. However, in either method, a satisfactory tonal rendition can only be obtained with a large threshold value matrix, the use of which however, results in a low resolution or in an image texture with marked periodicity of the threshold matrixes. Consequently, an image of a high quality cannot be obtained.
In order to avoid the above-mentioned drawback, it is conceivable, in the dither method, to obtain multi-level dot information through the use of plural dither matrixes. However, such method requires a complex circuit structure in order to synchronize different dither matrixes, and inevitably gives rise to a large and complicated system. Consequently such method is associated with a certain limitation.
Processing of image information is preferably conducted in a multi-level state where the number of bits per pixel is large, but a limited number of bits per pixel is desirable for transmission or storage of image information.
Also it is already known that a correction of a digital input image signal to a desired contrast results in a loss in the number of tonal levels. In order to overcome such drawback it is possible to expand the dynamic range of the input image signal by increasing the number of bits of said image signal, but such increase in the amount of information of the input image signal not only results in the increase in the number of signal lines but also requires a complex and inevitably expensive structure for information storage or processing.